1. Field of Invention
The present invention relates to a paper pickup and feeding apparatus, and more particularly, to a paper feeding apparatus for flipping a double-sided document sheet to scan or print both sides of the sheet, and maintaining paper feeding speed as scanning or printing a one-sided document sheet.
2. Related Art
In a printing apparatus having a single printing module, only one side of a paper sheet is printed at one time, when both sides of a paper sheet need to be printed, the paper sheet must be fed again after the printing of one side of the paper is complete, so as to print the other side of the paper sheet. In a scanning apparatus having a single scanning module, the process of double side scanning is similar, that is, one side of the paper sheet has to be scanned first before the other side is scanned.
In early double side printing or scanning method, the paper is flipped manually by a user and then fed into the paper feeding track again after one side has been printed or scanned, so as to perform the printing or scanning of the other side. However, this method is complex, and the printing or scanning directions of two sides of the paper are often different because of wrong manual operations. Therefore, in order to facilitate the double side scanning or printing and avoid problems caused by manual paper flipping, various paper feeding apparatuses have been proposed, in which a paper can be flipped automatically to pass through the printing or scanning module again after the printing or scanning of one side of the paper is complete, so as to perform the printing or scanning of the other side. For example, U.S. Pat. No. 5,430,536, No. 5,680,204, and No. 6,563,611 are paper feeding apparatuses for flipping the paper sheet to perform the double side printing or scanning.
In U.S. Pat. No. 5,430,536, an intersected path connects the front and rear sections of the paper feeding path. After the first side of the paper sheet is printed or scanned, the paper feeding apparatus reverses to move the paper sheet back, such that the paper returns to the original paper feeding path through the intersected path, such that the second side of the paper sheet is printed or scanned. Using the intersected path to reverse the paper sheet leads the paper sheet to pass the paper feeding path twice before the paper is flipped to be printed or scanned on both sides.
In U.S. Pat. No. 5,680,204, two scanning or printing modules are disposed on both sides of the paper feeding path to scan or print both sides of a paper sheet at the same time. However, though the paper feeding apparatus is simplified, two scanning or printing modules are used, thus greatly increase the cost.
In U.S. Pat. No. 6,032,949, a flipping path is used to flip the paper with the other side facing the scanning or printing module to complete the scanning or printing after the paper passes through the scanning or printing module. However, as the paths of the paper entering and leaving the paper feeding track are the same one, the paper feeding track can carry only one paper sheet at one time. When the single side of a paper sheet is scanned or printed, the paper feeding speed is lowered due to that another paper sheet is not allowed to entering the paper feeding track. In other words, the paper feeding speed of one-side scanning or printing is greatly influenced.
As conventional paper feeding apparatuses for double side scanning or printing have problems of low paper feeding speed or high cost, it has become the most important technical subject to improve the paper feeding speed and to reduce the cost.